The growth of the Internet and similar local and wide area networks (LAN and metropolitan ones) based on Ethernet technology has created a potential market for telecommunications systems to be connected directly to such networks. A typical Ethernet connection to an office location with a telecommunications system is usually based on the use of half of the 8 wires of a line L separated in two unshielded twisted pair of wires giving—one pair for transmission Tx, one for reception Rx. The transmission pair is dedicated to send packets of data over the Ethernet connection; the reception pair receives packets of data over the Ethernet connection. The four other wires are usually not used for data transmission but could also be used in a similar way.
At the IEEE committee 802.3 (Ethernet) was set a project 802.3af concerning remote powering of data terminal equipment DTE connected to an Ethernet interface i.e. a DTE powered by a media dependent interface MDI. There is discussed the possibilities and feasibility to remotely power a terminal via center taps using two pairs of wires of the line L as conductors of a phantom circuit. Particularly in U.S. Pat. No. 6,115,468 is disclosed an Ethernet device power transmission system providing electrical power to telecommunications terminals such as Ethernet telephones and related equipment over a 4-wire Ethernet connection. This is achieved without the need for rewiring premises having an existing 4-wire Ethernet system. This system includes an input transformer, an output transformer and a pair of twisted pair conductors. The input transformer includes a pair of primaries for connection to a source of Ethernet data. The input transformer also includes a pair of secondaries, each having a center-tap. A first twisted pair conductor is connected across the first secondary, a second twisted pair conductor is connected across the second secondary and a DC-bias is provided between the respective center taps of the first and second secondaries. At the local end, the output transformer includes a first and second center-tapped primary and a first and second secondary for connection to the load device. The first and second primary center taps are connected to a power processor for extraction of DC power.
In EP1100226 is disclosed a more specific method of providing a remote power feed to a telecommunications terminal over an Ethernet connection. Previously sending a power supply current over that connection, at least one detection signal on at least two conductors of that connection is fed for detecting the presence of a telecommunications terminal adapted to receive a remote power feed. Applying such method shall prevent all risk to such terminal because the remote power feed current is sent only if the terminal has been identified as one which is adapted to receive a remote power feed. The intensity and duration of the detection signal are chosen so that the operation of detecting the terminal cannot cause any damage if it is not one which is adapted to receive a remote power fed.
In a further development described in U.S. Pat. No. 5,555,274, similar signals can be used to build a phantom (out of band) data link for performance monitoring information. It allows a telephone company central offices and a remote location to communicate with each other over existing telephone lines, without interfering with, or displacing any telephone communications being sent over the lines. In U.S. Pat. No. 6,147,963 is discussed the use of such phantom data link for transmitting and receiving dc balanced data strobe signals. This enables to distribute power via the phantom circuit as well as data under the control of a continuously variable clock. In such a way, it is possible to synchronize all the terminals connected to such phantom data link.
In WO 00/41496 is described the application of remote powering on a local area network. Such network includes a hub, a plurality of nodes, communications cabling connecting the plurality of nodes to the hub for proving data communications, and a power supply distributor operative to provide at least some operating power to at least some of the plurality of nodes via the communication cabling. The hub has a data communication concentrator which is connected to each node through a combiner of the power supply, by the communication cabling. The data communication concentrator is provided for transmitting data to each node through the cabling, while the combiner supplies power to each node through the cabling. That powering managed by the combiner is controlled via some electrical gates activated by a controller. The latter receives control input from a sensor which may be implemented in a number of possible ways. One is such that it may sense a control signal transmitted in phantom mode via the communications cabling from the power management.